Amber weather warnings are in place for heavy snow across most of Scotland, Northern Ireland and northern England.
Snow is already affecting parts of northern Scotland and will head southwards during Wednesday.
More than 5cm is expected at lower levels but there could be as much as 15cm on higher ground.
BBC weather expert Simon King told Newsround: "With the cold air really digging in there is a chance of 5-10cm falling and settling at low levels."
The weather forecasters at the Met Office said: "The public should be prepared for travel disruption and hazardous driving conditions."
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